1. Field of the Invention
The present invention relates to a switch for use in a fiber optic communications network and, in particular, to a switch for a network using single mode fibers wherein the movable and fixed members of the switch are fabricated from glass.
2. Description of the Prior Art
Telecommunication systems using fiber optic cable as the medium for transmission of information are rapidly displacing systems that use metallic wires as the transmission medium. In fabricating such systems the ability to switch light from one fiber optic cable to another is important for system operation.
Devices are known which allow the switching connection of one fiber to another. Exemplary of such devices are those described in U.S. Pat. Nos. 4,416,856 and Re. 31,579 (both to Jaeschke) and U.S. Pat. No. 4,452,507 (Winzer). Each of the switches disclosed in these patents includes magnetically responsive switching elements. U.S. Pat. No. 4,303,302 (Ramsey et al.) discloses a piezoelectric actuated switching element. U.S. Pat. No. 4,223,978 (Kummer et al.) shows a motor actuated rotatably driven switching element.
These switches are all believed to be disadvantageous, particularly when the fiber optic system is implemented using single mode fiber, because they are not capable of providing, for extended periods over a large number of operating cycles, the precise end-to-end alignment of the fibers needed to achieve a low loss connection. A magnetically responsive switching device, which must of necessity use a metallic movable switch element, is believed unable to provide the necessary long term alignment because of the susceptibility of the metallic element to creep and fatigue. A piezoelectric switch requires a source of precise actuating voltage to achieve the desired deflection of the switching element. Providing such a source may be difficult. In addition piezoelectric elements are also known to creep over time. The rotary switch arrangement is susceptible to frictional wear, which will degrade alignment over the lift of the switch.
In view of the foregoing it is believed advantageous to provide a switch for coupling optical fibers, especially single mode optical fibers, with a repeatably reproducible low insertion loss such that, once the fibers are aligned, the alignment is retained over an extended lifetime and/or over millions of operations cycles of the switch. It is also believed to be advantageous to provide a switch which uses as the switching elements a material that has surfaces readily processable to wavelength tolerances (to achieve the desired fiber-to-fiber alignment) and which is transparent to both visible and UV radiation. Both of these latter considerations enhance the manufacturability of the switch. It is believed advantageous to use a material which closely obeys Hooke's Law, has a low coefficient of thermal expansion and an isotropic expansion characteristic.